Understanding how SolarStratos flies on solar power, without a single drop of kerosene.
What is solar-electric aviation?
Imagine an aircraft… that flies without fuel. No kerosene, almost no noise, and energy that comes directly from the sun. This is exactly the principle behind solar-electric aviation. And no, it’s not science fiction — it’s what SolarStratos has been doing from Payerne, Switzerland, for several years already.
The basic principle in three steps
The way it works is actually quite intuitive:
1. Photovoltaic cells are integrated into the aircraft’s wings
2. They capture solar energy and convert it into electricity
3. This electricity powers an electric motor that drives the propeller
And the surplus energy produced? It’s stored in onboard batteries, to be used when sunlight is no longer enough.
Think of an electric bike: the solar panel is the dynamo. The battery is the small energy reserve. And the motor is what moves you forward. Except that here, we’re at an altitude of 10,000 metres.
The concrete case of SolarStratos
This is where it gets really interesting. SolarStratos is no ordinary aircraft. It’s a two-seater solar and electric, designed to reach the stratosphere — that layer of the atmosphere located far above the cruising altitude of an airliner. A breathtaking ambition, made possible by highly precise energy management.
Two-stage energy management
1. During the day: produce and fly
As soon as the sun shines, the solar cells integrated into the wings spring into action:
- They directly power the motor to sustain flight
- At the same time, they recharge the batteries
- The goal: produce more energy than is consumed
We fly and refuel at the same time. Like an electric car that recovers energy when braking, but in a solar version, and continuously.
2. At high altitude or without sun: the batteries take over
As the aircraft climbs, atmospheric pressure drops and conditions become harsher. When solar production is no longer sufficient, the lithium-ion batteries take over.
These are no ordinary batteries. They are:
- Ultra-lightweight: every gram counts when you’re trying to climb high
- Optimised for high altitude: they must operate under low atmospheric pressure
- Resistant to extreme cold: the aircraft operates in outside temperatures that can drop as low as -60°C
The key balance: the real challenge of SolarStratos
Flying on solar power is simple on paper. In practice, it’s an exercise in constant balance between four constraints:
Every flight is a real-time optimisation. The pilot, Raphaël Domjan, constantly manages these parameters to ensure the aircraft reaches its destination with enough energy… and without ever exceeding the limit.
It’s a bit like crossing a city in an electric car with an uncertain state of charge, at -50°C, going uphill, and with no permission to stop along the way.
Why aim for the stratosphere?
SolarStratos isn’t just trying to fly. It’s trying to climb where no one has ever gone in a manned solar-electric aircraft.
In the stratosphere:
- The air becomes so thin that it represents only a tiny fraction of the density at sea level
- Outside temperatures are freezing
- Conditions approach those found at the edge of space
- Solar radiation is at its maximum: with a much thinner atmosphere to filter the rays, the solar panels come close to their optimal efficiency
It’s a hostile environment for humans… but ideal for demonstrating the power of solar energy.
Reaching the stratosphere with a manned solar-electric aircraft means proving that this technology can operate under extreme, measurable, and reproducible conditions, far beyond low-altitude demonstrations.
A flying laboratory
SolarStratos isn’t here to replace an Airbus overnight. Its role lies elsewhere: to test, validate, and demonstrate.
Every flight generates valuable data on:
- Battery behaviour under extreme conditions
- The efficiency of solar cells at high altitude
- The thermal management of onboard systems
- The aerodynamic performance of an ultra-light aircraft
This data fuels research, inspires engineers, and paves the way for future applications in sustainable aviation.
In summary, the key takeaways
Energy source: sun + lithium-ion batteries
How it works: produce during the day, use continuously
Role of the batteries: stabilise the flight when sunlight isn’t enough
The real challenge: constant energy balance
Goal: reach the stratosphere with zero emissions
Impact: a flying laboratory for the aviation of tomorrow
SolarStratos doesn’t just fly to get from point A to point B. It flies to prove that yesterday’s impossible can become tomorrow’s standard.
Spotlight
Rediscover our spotlight on SolarStratos’s energy management!
